Single-atom photocatalysts have shown their compelling potential and arguably become the most active research direction in photocatalysis due to their fascinating strengths in enhancing light-harvesting, charge transfer dynamics, and surface reactions of a photocatalytic system. While numerous comprehensions about the single-atom photocatalysts have recently been amassed, advanced characterization techniques and vital theoretical studies are strengthening our understanding on these fascinating materials, allowing us to forecast their working mechanisms and applications in photocatalysis. In this review, we begin by describing the general background and definition of the single-atom photocatalysts. A brief discussion of the metal-support interactions on the single-atom photocatalysts is then provided. Thereafter, the current available characterization techniques for single-atom photocatalysts are summarized. After having some fundamental understanding on the single-atom photocatalysts, their advantages and applications in photocatalysis are discussed. Finally, we end this review with a look into the remaining challenges and future perspectives of single-atom photocatalysts. We anticipate that this review will provide some inspiration for the future discovery of the single-atom photocatalysts, manifestly stimulating the development in this emerging research area.

Heterogeneous Single-Atom Photocatalysts: Fundamentals and Applications.

Emerging single atom catalysts (SACs), especially carbon-based SACs are appealing materials in environmental catalysis because of their ultrahigh performances, environmental friendliness, structural/chemical robustness, and the maximum utilization of active metal sites. The metal centres, carbon matrixes, and coordination characteristics collectively determine the electronic features of carbon-based SACs, and their behaviours in catalysing peroxide activation and efficiencies in advanced oxidation processes (AOPs). However, there is lack of a comprehensive and critical review reporting the successful marriage of carbon-based SACs in AOP-based remediation technologies. It is particularly necessary to systematically compare and reveal the catalytic sites and the associated mechanisms of carbon-based SACs in diverse AOP systems. In this review, we highlight the synthetic strategies, characterisation, and computation of carbon-based SACs, and for the first time, showcase their innovative applications in AOP technologies. We unveil the origins of versatile catalytic oxidation pathways in different AOP systems and the mechanisms of micropollutant degradation over carbon-based SACs, distinguished from the upsized counterparts (metals/oxides and carbon substrates). We also provide directions to the rational design of on-demand SACs for green chemistry and environmental sustainability. Also, we suggest a designated and integrated experimental/theoretical protocol for revealing the structure-catalysis relations of SACs in AOP applications, and propose the prospects for future opportunities and challenges.

Single-atom catalysis in advanced oxidation processes for environmental remediation.

Metal atoms dispersed on the oxide supports constitute a large category of single-atom catalysts. In this review, oxide supported single-atom catalysts are discussed about their synthetic procedures, characterizations, and reaction mechanism in thermocatalysis, such as water-gas shift reaction, selective oxidation/hydrogenation, and coupling reactions. Some typical oxide materials, including ferric oxide, cerium oxide, titanium dioxide, aluminum oxide, and so on, are intentionally mentioned for the unique roles as supports in anchoring metal atoms and taking part in the catalytic reactions. The interactions between metal atoms and oxide supports are summarized to give a picture on how to stabilize the atomic metal centers, and rationally tune the geometric structures and electronic states of single atoms. Furthermore, several directions in fabricating single-atom catalysts with improved performance are proposed on the basis of state-of-the-art understanding in metal-oxide interactions.

Single-Atom Catalysts Based on the Metal-Oxide Interaction.

Most organic compounds are conventionally synthesized under high temperature and elevated pressure, resulting in significant energy consumption and wastage. Heterogeneous photocatalytic oxidation has the potential to provide a green route for the synthesis of the majority of industrially important chemicals. The major limiting factor affecting the efficiency of photocatalytic organic synthesis is the lack of high selectivity; therefore, substantial effort has been devoted to solving this problem. Responding to this fast-moving progress, this review gives an overview of the fundamental understanding of the reactive oxygen species involved in photocatalytic organic oxidations and furthermore, the general mechanisms of a few crucial oxidation reactions. The focus of this critical review is on the discussion of diverse strategies to improve the selectivity of high value chemicals, including band engineering, metal loading, hybrid materials, and defect engineering, with the primary aim of highlighting the catalyst design protocols based on the reaction mechanism. Finally, the difficulties and challenges of developing highly selective oxidation photocatalysts are comprehensively discussed in order to help direct the focus of future research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/aenm.202003216

Strategies and Challenges on Selectivity of Photocatalytic Oxidation of Organic Substances

Single-atom catalysts for photocatalytic energy conversion

The dehalogenation–arylation and the hydrodehalogenation of various types of organic halides are selectively realized using AgF and visible light without any organic additives under mild conditions...

Involving Single-Atom Silver(0) in Selective Dehalogenation by AgF under Visible-Light Irradiation

Plasmon stimulation represents an appealing way to modulate enzyme mimic functions, but utilization efficiency of plasmon excitation remains relatively low. To overcome this drawback, a heterojunction composite based on graphdiyne nanowalls wrapped hollow copper sulfide nanocubes (CuS@GDY) with strong localized surface plasmon resonance (LSPR) response in the near‐infrared (NIR) region is developed. This nanozyme can concurrently harvest LSPR induced hot carriers and produce photothermal effects, resulting in dramatically increased peroxidase‐like activity when exposed to 808 nm light. Both experimental results and theoretical calculations show that the remarkable catalytic performance of CuS@GDY is due to the unique hierarchical structure, narrow bandgap of GDY nanowalls, LSPR effect of CuS nanocages, fast interfacial electron transfer dynamics, and carbon vacancies on CuS@GDY. This plasmonic nanozyme exhibits rapid, efficient, broad‐spectrum antibacterial activity (>99.999%) against diverse pathogens (methicillin‐resistant Staphylococcus aureus, Staphylococcus aureus, and Escherichia coli). This study not only sheds light on the mechanism of the nanozyme‐/photocatalysis coupling process, but also opens up a new avenue for engineering plasmonic NIR light driven nanozymes for rapid synergistic photothermal and photo‐enhanced nanozyme therapy.

Wenli Wu

Papers

Involving Single-Atom Silver(0) in Selective Dehalogenation by AgF under Visible-Light Irradiation

Plasmonic Nanozyme of Graphdiyne Nanowalls Wrapped Hollow Copper Sulfide Nanocubes for Rapid Bacteria‐Killing

Selective endoperoxide formation by heterogeneous TiO2 photocatalysis with dioxygen

Colorimetric liquid crystal-based assay for the ultrasensitive detection of AFB1 assisted with rolling circle amplification.

A paper-based lateral ﬂow sensor for the detection of thrombin and its inhibitors.